NFT balance, Arbitrum. How many NFTs of one ERC-721 collection a wallet holds on Arbitrum One (balanceOf), with the collection's name and symbol. Use to check a holder before a token-gated action or to see whether a wallet still holds a collection; for who holds one token id use arb_nft_owner. Both inputs are 0x addresses; a missing contract is 404, a contract that is not ERC-721 422, both uncharged.